KR20210111812A - Method for manufacturing grain-oriented electrical steel sheet - Google Patents

Abstract

This method for producing a grain-oriented electrical steel sheet includes an intermediate layer containing silicon oxide as a main component on the surface of a mother steel sheet substantially free of a forsterite film, and a method for producing a grain-oriented electrical steel sheet having an insulating film on the surface of the intermediate layer, A decarburization annealing process for performing decarburization annealing on a cold-rolled steel sheet containing Si to obtain a decarburization annealing steel sheet having an oxygen content of 320 ppm or less and a carbon content of 25 ppm or less; A finish annealing step of heating the decarburization annealed steel sheet to secondary recrystallize the steel sheet, a removal step of removing an annealing separator on the steel sheet after the finish annealing step to obtain a finish annealing steel sheet, and performing thermal oxidation annealing on the finish annealing steel sheet It has an intermediate|middle layer formation process of forming an intermediate|middle layer, and the insulating-film formation process of forming an insulating film on the finish-annealing steel plate in which the said intermediate|middle layer was formed.

Description

Method for manufacturing grain-oriented electrical steel sheet

The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet substantially free of a forsterite coating.

This application claims priority based on Japanese Patent Application No. 2019-005399 for which it applied to Japan on January 16, 2019, and uses the content here.

A grain-oriented electrical steel sheet is widely used as a magnetic iron core material, and in particular, a material with low iron loss is required in order to reduce energy loss. As a means for reducing iron loss, it is known that it is effective to apply tension to the surface of a steel sheet.

In order to impart tension to the steel sheet, it is effective to form a film made of a material having a smaller coefficient of thermal expansion than that of the steel sheet at a high temperature. The finish annealing film (forsterite film) generated by the reaction between the oxide on the surface of the steel sheet and the annealing separator in the finish annealing process can impart tension to the steel sheet and has excellent film adhesion.

On the other hand, in recent years, it has been found that the disordered interfacial structure between the finish annealing film and the base iron counteracts the film tension effect on iron loss. Therefore, a technique for further reducing iron loss is proposed by obtaining a grain-oriented electrical steel sheet that has been mirror-finished during finish annealing by a method as disclosed in Patent Document 1 or Patent Document 2, and then applying a tension coating again. has been

Patent Document 1 discloses that the atmospheric oxidation degree P _H2O /P _H2 during heating is set to 0.01 to 0.15 in order to suppress the formation of iron-based oxides. Moreover, in patent document 2, it is demonstrated that it becomes possible to perform decarburization efficiently by making the heating rate to 770-860 degreeC 9 degreeC/s or more.

However, in these patent documents, the plate thickness at the time of decarburization annealing is performed at 0.14 mm and 0.23 mm, and the application technique to the thick material (0.23 mm or more) is not demonstrated.

Japanese Patent Laid-Open No. 07-118750 Japanese Patent Laid-Open No. Hei 07-278668

N. Morito et al: Scripta METALLURGICA, 10 (1976), 619-622

The present invention is a method for manufacturing a grain-oriented electrical steel sheet substantially free of a forsterite film, and provides a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties by both promoting decarburization and inhibiting oxidation of the steel sheet in a wide sheet thickness range. intended to provide

"1" A method for manufacturing a grain-oriented electrical steel sheet according to an aspect of the present invention includes an intermediate layer mainly composed of silicon oxide on a surface of a mother steel sheet substantially free of a forsterite film, and an insulating film on the surface of the intermediate layer A method for manufacturing a grain-oriented electrical steel sheet, comprising: a decarburization annealing step of performing decarburization annealing on a cold rolled steel sheet containing Si to obtain a decarburization annealing steel sheet having an oxygen content of 320 ppm or less and a carbon content of 25 ppm or less; A final annealing step of secondary recrystallization of the steel sheet by heating the decarburization annealed steel sheet in a state in which an annealing separator is applied; An intermediate layer forming step of forming the intermediate layer by subjecting the finish annealed steel sheet to thermal oxidation annealing, and an insulating film forming step of forming the insulating film on the finish annealing steel sheet on which the intermediate layer is formed.

[2] In the method for manufacturing a grain-oriented electrical steel sheet according to another aspect of the present invention, an intermediate layer containing silicon oxide as a main component is provided on a surface of a mother steel sheet substantially free of a forsterite film, and an insulating film is provided on the surface of the intermediate layer. A method for manufacturing a grain-oriented electrical steel sheet, comprising: a decarburization annealing step of performing decarburization annealing on a cold rolled steel sheet containing Si to obtain a decarburization annealing steel sheet having an oxygen content of 320 ppm or less and a carbon content of 25 ppm or less; A final annealing step of secondary recrystallization of the steel sheet by heating the decarburization annealed steel sheet in a state in which an annealing separator is applied; and an intermediate layer-insulating film forming process in which the intermediate layer and the insulating film are formed in one step on a finish annealed steel sheet.

"3" In the method for manufacturing a grain-oriented electrical steel sheet according to "1" or "2" above, in the decarburization annealing step, atmospheric gas is applied to a crack zone for decarburization annealing of the cold-rolled steel sheet at the front end of the crack zone and You may introduce|transduce from two places of the rear stage.

"4" In the method for manufacturing a grain-oriented electrical steel sheet according to "3" above, in the decarburization annealing step, the dew point DP1 of the atmospheric gas introduced from the front end of the cracking zone is 40 to 70°C, and from the rear end of the cracking zone The dew point DP2 of the atmospheric gas to be introduced may be DP2 ? DP1 and 60-DP1 ? DP2 ? 100-DP1.

"5" In the method for manufacturing a grain-oriented electrical steel sheet according to any one of "1" to "4", the cold-rolled steel sheet contains, as a chemical component, in mass%, Si: 0.80 to 7.00%, C: 0.085% or less; Acid soluble Al: 0.010 to 0.065%, N: 0.012% or less, Mn: 1.00% or less, the sum of S and Se: 0.003 to 0.015%, and the balance may consist of Fe and impurities.

According to the above aspect of the present invention, it is possible to provide a method for manufacturing a grain-oriented electrical steel sheet substantially free of a forsterite film. In the method for manufacturing a grain-oriented electrical steel sheet according to the above aspect, by achieving both decarburization and steel sheet oxidation suppression in a wide sheet thickness range, a grain-oriented electrical steel sheet with low iron loss and high magnetic flux density after magnetic aging can be manufactured.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the relationship between the oxygen amount [O] of the steel plate after decarburization annealing, and the iron loss of a final product.
2 is a diagram showing the relationship between the carbon content [C] of the steel sheet after decarburization annealing, the aging time of the final product, and the magnetic flux density (B8).
3 is a view showing the effect of the oxidation degree (P _H2O /P _H2 ) of the gas on the oxide layer of the steel sheet after decarburization annealing.
4A is a block diagram in the case of introducing atmospheric gas only from the rear end of the crack zone in the decarburization annealing furnace.
Fig. 4B is a configuration diagram in the case of introducing atmospheric gas from two locations of a front end and a rear end of a crack zone in a decarburization annealing furnace.
It is explanatory drawing which shows the outline|summary of the dew point distribution of the atmospheric gas in the furnace at the time of using the decarburization annealing furnace of FIG. 4A or FIG. 4B.
Fig. 5 is a diagram showing the relationship between magnetic properties and dew points (front-end dew point DP1 and rear-end dew point DP2).

As described above, the disordered interfacial structure between the forsterite film and the iron offsets the film tension effect on iron loss. Therefore, the present inventors proceeded to study a method for producing a grain-oriented electrical steel sheet substantially free of a forsterite film. In addition, in a grain-oriented electrical steel sheet substantially free of a forsterite film, in order to secure the adhesion of the insulation film, an intermediate layer containing silicon oxide as a main component is formed on the surface of the mother steel sheet, and an insulation film is formed on the surface of the intermediate layer. The manufacturing method was assumed.

As a result of the investigation by the present inventors, in the method for manufacturing a grain-oriented electrical steel sheet having an intermediate layer containing silicon oxide as a main component on the surface of the mother steel sheet substantially free of the forsterite film, and having an insulating film on the surface of the intermediate layer, decarburization annealing In the process, by processing under specific conditions and adjusting the amount of oxygen and the amount of carbon in the steel sheet after decarburization to specific ranges, decarburization and oxidation of the steel sheet can be achieved in a wide range of thickness, thereby providing a grain-oriented electrical steel sheet having excellent magnetic properties I found out what I can do.

Hereinafter, the grain-oriented electrical steel sheet manufactured by the method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention (the manufacturing method of the grain-oriented electrical steel sheet according to the present embodiment) and the grain-oriented electrical steel sheet according to the present embodiment It will be described in detail.

In the following description, when a numerical range is expressed as "a lower limit to an upper limit," it means "above the lower limit and below the upper limit" unless otherwise specified.

A. Grain-oriented electrical steel sheet

A grain-oriented electrical steel sheet (hereinafter, sometimes referred to as a grain-oriented electrical steel sheet of this embodiment) produced by the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment includes a mother steel sheet, an intermediate layer containing silicon oxide as a main component, and insulation It is a grain-oriented electrical steel sheet having a three-layer structure having a coating film in this order.

Hereinafter, the basic structure of the three layers of the grain-oriented electrical steel sheet of the present embodiment will be described.

1-1. mother steel plate

An electrical steel sheet (grain-oriented electrical steel sheet of this embodiment) manufactured by the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment has an insulating film in contact with an intermediate layer mainly made of silicon oxide, The chemical composition, structure, and the like of the mother steel sheet in the present invention are not directly related to the layer structure of the insulating film except that Si is contained as an essential component. For this reason, the mother steel sheet in the grain-oriented electrical steel sheet of this embodiment is not particularly limited as long as the effect required in the present embodiment is obtained, for example, a mother steel sheet in a general grain-oriented electrical steel sheet can be used. . Hereinafter, the mother steel sheet in the grain-oriented electrical steel sheet of this embodiment is demonstrated.

(1) chemical composition

For the chemical composition of the mother steel sheet, for example, except for containing Si as an essential component, the chemical composition of the mother steel sheet in a general grain-oriented electrical steel sheet can be used. Since the function of Si is the same as that of a general grain-oriented electrical steel sheet, the content may be determined within a general range from the characteristics required for the target grain-oriented electrical steel sheet.

Below, content of each component in the chemical composition of a mother steel plate is a value in mass %. Further, the chemical composition of the grain-oriented electrical steel sheet of the present embodiment is stable at a depth of 50 to 60 µm.

A typical example of the chemical composition of the mother steel sheet is, in mass%, Si: 0.80% to 7.00%, and Mn: 0.05% to 1.00%, and the balance consists of Fe and impurities. Moreover, in addition to the said chemical composition, you may contain 0.003 % or more and 0.015 % or less of S and Se in total. Hereinafter, the reason for limitation of a typical example of a chemical composition is demonstrated.

"Si": 0.80% or more and 7.00% or less

Si is an essential component and increases electrical resistance to decrease iron loss. Moreover, by containing Si at a high concentration, strong chemical affinity is expressed between the intermediate|middle layer which has silicon oxide as a main body, and an intermediate|middle layer and a mother steel plate closely_contact|adhere more strongly. However, when content of Si exceeds 7.00 %, cold rolling becomes very difficult, and it becomes easy to generate|occur|produce a crack at the time of cold rolling. For this reason, it is preferable to make content of Si into 7.00 % or less. More preferably, it is 4.50 % or less, More preferably, it is 4.00 % or less.

On the other hand, when the content of Si is less than 0.80%, γ transformation occurs at the time of finish annealing, and the preferable crystal orientation of the grain-oriented electrical steel sheet is impaired. For this reason, it is preferable that content of Si shall be 0.80 % or more. More preferably, it is 2.00 % or more, More preferably, it is 2.50 % or more.

"Mn": 0.05% or more and 1.00% or less

"S and Se": 0.003% or more and 0.015% or less in total

Mn, together with S and Se, forms MnS and MnSe, and the complex compound functions as an inhibitor. When the Mn content is within the range of 0.05% to 1.00%, secondary recrystallization is stable. For this reason, it is preferable that content of Mn shall be 0.05 % - 1.00 %. As for content of Mn, it is more preferable that it is 0.08 % or more, and it is still more preferable that it is 0.09 % or more. Moreover, it is more preferable that it is 0.50 % or less, and, as for content of Mn, it is still more preferable that it is 0.20 % or less.

"Remainder"

The remainder consists of Fe and impurities. "Impurity" means an element that is unavoidably mixed from a component included in a raw material or a component mixed in a manufacturing process when a mother steel sheet is industrially manufactured.

1-2. mezzanine

The intermediate layer is formed on the surface of the mother steel sheet and contains silicon oxide as a main component. In the grain-oriented electrical steel sheet of the present embodiment, since it does not substantially have a forsterite film, the intermediate layer is formed in direct contact with the surface of the mother steel sheet. The intermediate layer has a function of bringing the base steel sheet into close contact with the insulating coating in the three-layer structure of the present embodiment.

In the grain-oriented electrical steel sheet of the present embodiment, the intermediate layer means a layer present between the mother steel sheet to be described later and an insulating film (compound layer to be described later) described later.

The main component of the intermediate layer silicon oxide, is more preferable SiO _{x (x} = 1.0 to 2.0) are preferable, SiO _{x (x} = 1.5 to 2.0). This is because silicon oxide is more stable. When the heat treatment for forming silicon oxide on the surface of the steel sheet is sufficiently performed, silica (SiO ₂ ) can be formed.

The silicon oxide as a main component means that the composition of the intermediate layer has a Fe content of less than 30 atomic%, a P content of less than 5 atomic%, a Si content of 20 atomic% or more, an O content of 50 atomic% or more, and a Mg content, as will be described later. It satisfies this 10 atomic% or less.

When the intermediate layer is thin, the thermal stress relaxation effect is not sufficiently exhibited, so that film adhesion cannot be ensured. Therefore, 2 nm or more is preferable and, as for the thickness of an intermediate|middle layer, 5 nm or more is more preferable. On the other hand, when an intermediate|middle layer is thick, while thickness becomes non-uniform|heterogenous, there is a concern that defects, such as a void and a crack, generate|occur|produce in a layer. Therefore, 400 nm or less is preferable and, as for the thickness of an intermediate|middle layer, 300 nm or less is more preferable. In addition, if the thickness of the intermediate layer is made within a range that can ensure film adhesion, the formation time can be shortened, which can contribute to high productivity and suppress a decrease in the space factor when used as an iron core. Therefore, 100 nm or less is more preferable, and 50 nm or less is more preferable.

Although the method for measuring the thickness and position of the intermediate layer is not particularly limited, for example, using an SEM (scanning electron microscope) or TEM (transmission electron microscope) with an electron beam diameter of 10 nm, the cross section of the intermediate layer is observed as follows. It can be obtained by measuring.

Specifically, the test piece is cut by FIB (Focused Ion Beam) processing so that the cut surface is parallel to the sheet thickness direction and perpendicular to the rolling direction, and the cross-sectional structure of this cut surface is STEM ( Scanning-TEM) (bright field image). When each layer does not enter in an observation visual field, the cross-sectional structure is observed in several continuous visual fields.

In order to specify each layer in a cross-sectional structure, using TEM-EDS (Energy Dispersive X-ray Spectroscopy), line analysis is performed along the plate|board thickness direction, and the chemical component of each layer is quantitatively analyzed. In the observation cross section of the sample, 100 locations were measured at intervals of 0.1 µm in a direction parallel to the surface of the mother steel plate. At this time, quantitative analysis is performed at intervals of 1 nm in the plate thickness direction by energy dispersive X-ray spectroscopy (EDS) in which the diameter of the electron beam is 10 nm.

Elements to be quantitatively analyzed are five elements of Fe, P, Si, O, and Mg. In addition, identification of the crystal phase by electron beam diffraction is performed together with EDS for identification of a compound layer.

Each layer is specified from the bright field image observation by TEM, quantitative analysis of TEM-EDS, and electron beam diffraction result, and the thickness of each layer is measured. Subsequent measurement of each layer and thickness are all performed on the same scanning line of the same sample.

The region where the Fe content is 80 atomic% or more is judged as the mother steel sheet. The region where the Fe content is less than 80 atomic%, the P content is 5 atomic% or more, the Si content is less than 20 atomic%, the O content is 50 atomic% or more, and the Mg content is 10 atomic% or less is judged as an insulating film. In addition, the region where the Fe content is less than 30 atomic%, the P content is less than 5 atomic%, the Si content is 20 atomic% or more, the O content is 50 atomic% or more, and the Mg content is 10 atomic% or less is judged as the intermediate layer. .

When each layer is judged as a component as described above, a region (blank region) that does not correspond to any composition in the analysis may occur. However, in the grain-oriented electrical steel sheet of the present embodiment, each layer is specified so as to have a three-layer structure of a mother steel sheet, an intermediate layer, and an insulating film (including a composition change layer). The judgment criteria are as follows.

First, the blank region between the mother steel plate and the intermediate layer is regarded as the mother steel plate on the mother steel plate side and the intermediate layer on the intermediate layer side with the center of the blank region as a boundary in the thickness direction. Next, the blank region between the insulating film and the intermediate layer is regarded as the insulating film on the side of the insulating film and the intermediate layer on the side of the intermediate layer with the center in the thickness direction of the blank region as a boundary. By this procedure, the mother steel sheet, the insulating film, and the intermediate layer can be separated.

1-3. insulation film

The insulating film is formed on the surface of the intermediate layer, and in addition to reducing iron loss as a steel sheet single sheet by applying tension to the steel sheet, it has a function of securing electrical insulation between grain-oriented electrical steel sheets when laminated and used.

The composition of the insulating film is not particularly limited, and can be appropriately selected from known ones depending on the application and the like, and either an organic film or an inorganic film may be used.

Examples of the organic film include polyamine resins, acrylic resins, acrylic styrene resins, alkyd resins, polyester resins, silicone resins, fluororesins, polyolefin resins, styrene resins, vinyl acetate resins, epoxy resins, phenol resins, urethane resins, A melamine resin etc. are mentioned. Examples of the inorganic coating include a phosphate-based coating, an aluminum phosphate-based coating, and an organic-inorganic composite coating containing the above resin. More specifically, it may bake what disperse|distributed the particle|grains of colloidal silica in the matrix. Here, a "matrix" means the substrate of an insulating film, and is comprised, for example from amorphous phosphate. Examples of the amorphous phosphate constituting the matrix include aluminum phosphate and magnesium phosphate. The insulating film after baking consists of several compounds containing 1 or more types of P, O, and S.

When an insulating film becomes thin, while the tension|tensile_strength given to a steel plate becomes small, insulation also falls. Therefore, 0.1 micrometer or more is preferable and, as for the thickness of an insulating film, 0.5 micrometer or more is more preferable. On the other hand, if the thickness of the insulating film exceeds 10.0 µm, cracks may occur in the insulating film at the stage of forming the insulating film. Therefore, the thickness of the insulating film is preferably 10.0 µm or less, and more preferably 5.0 µm or less.

If necessary, the insulating film may be subjected to a magnetic domain refining process for forming a local micro-strain region or groove by laser, plasma, mechanical method, etching, or other method.

B. Manufacturing method of grain-oriented electrical steel sheet

Next, a method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment will be described.

The manufacturing method of the grain-oriented electrical steel sheet according to the present embodiment is described in "A. A method for producing a grain-oriented electrical steel sheet having an intermediate layer containing silicon oxide as a main component on the surface of the mother steel sheet substantially free of the forsterite film described in the item of " grain-oriented electrical steel sheet" and having an insulating film on the surface of the intermediate layer. In other words, it is a method for manufacturing a grain-oriented electrical steel sheet having a mother steel sheet, an intermediate layer formed on the surface of the mother steel sheet, and an insulating film formed on the surface of the intermediate layer. Since the mother steel sheet does not have a forsterite film, the intermediate layer is formed in direct contact with the mother steel sheet.

"Manufacturing method of 1st embodiment"

In the method for manufacturing a grain-oriented electrical steel sheet according to the first embodiment, the intermediate layer and the insulating coating are formed in different steps. That is, the method for manufacturing a grain-oriented electrical steel sheet according to the first embodiment includes the following steps.

(I) a decarburization annealing step of performing decarburization annealing on a cold rolled steel sheet containing Si to obtain a decarburization annealing steel sheet having an oxygen content of 320 ppm or less and a carbon content of 25 ppm or less

(II) a final annealing process of secondary recrystallization of the decarburization annealing steel sheet by heating the decarburization annealing steel sheet in a state in which an annealing separator is applied to the surface of the decarburization annealing steel sheet

(III) A removal step of obtaining a finish annealing steel sheet by removing an annealing separator on the steel sheet (decarburization annealing steel sheet) after the final annealing step

(IV) an intermediate layer forming step of forming an intermediate layer by performing thermal oxidation annealing on the finish annealed steel sheet

(V) an insulating film forming step of forming an insulating film on the finish annealing steel sheet on which the intermediate layer is formed

"Manufacturing method of 2nd embodiment"

In the method for manufacturing a grain-oriented electrical steel sheet according to the first embodiment, the intermediate layer and the insulating film are simultaneously formed in one step. That is, the method for manufacturing a grain-oriented electrical steel sheet according to the second embodiment includes the following steps.

(I) a decarburization annealing step of performing decarburization annealing on a cold rolled steel sheet containing Si to obtain a decarburization annealing steel sheet having an oxygen content of 320 ppm or less and a carbon content of 25 ppm or less

(II) a final annealing process of secondary recrystallization of the decarburization annealing steel sheet by heating the decarburization annealing steel sheet in a state in which an annealing separator is applied to the surface of the decarburization annealing steel sheet

(III) A removal step of obtaining a finish annealing steel sheet by removing an annealing separator on the steel sheet (decarburization annealing steel sheet) after the final annealing step

(IV') Interlayer-insulation film forming process of forming an intermediate layer and an insulating film on the finish-annealed steel sheet in one process

In the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment, the interfacial unevenness of the finish annealing film and the base steel sheet prevents the effect of lowering iron loss by the insulating film from being hindered, and the intermediate layer improves the adhesion between the insulating film and the base steel sheet. can be obtained

Hereinafter, each step in the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment will be described, divided into the first embodiment and the second embodiment.

In the following, since conditions other than the above-described particularly characteristic steps are general conditions shown as examples, it is possible to obtain the effect of the present embodiment even if they are not satisfied.

B-1. first embodiment

1. Cold rolled steel sheet provided for decarburization annealing process

First, the cold-rolled steel sheet used for the decarburization annealing mentioned later is demonstrated.

The cold rolled steel sheet may have the chemical composition of the mother steel sheet in a general grain-oriented electrical steel sheet except for containing Si as an essential component. Since the function of Si in an electrical steel sheet is the same as that of a general grain-oriented electrical steel sheet, the content may be determined within a general range from the characteristics required for the intended electrical steel sheet.

For example, the chemical composition of the cold rolled steel sheet is, in mass%, Si: 0.80 to 7.00%, C: 0.085% or less, acid soluble Al: 0.010 to 0.065%, N: 0.012% or less, Mn: 1.00% or less, The sum total of S and Se: 0.003 to 0.015 % is contained, and the balance which consists of Fe and an impurity can be illustrated.

Such a cold-rolled steel sheet, for example, after heating a slab, is a hot-rolling step of performing hot rolling to obtain a hot-rolled steel sheet, a hot-rolled sheet annealing step of subjecting the hot-rolled steel sheet to hot-rolled sheet annealing to obtain an annealed steel sheet; , it can manufacture by the manufacturing method provided with the cold rolling process which cold-rolls the said annealing steel plate once or 2 times or more with intermediate annealing between them, and obtains a cold-rolled steel plate.

Since the chemical composition does not substantially change in slab heating, hot rolling, hot rolling annealing, and cold rolling, the slab is made according to a known technique according to the required chemical composition of the cold rolled steel sheet. A typical example of the chemical composition is, in mass%, Si: 0.80% to 7.00%, C: 0.085% or less, acid soluble Al: 0.010% to 0.065%, N: 0.004% to 0.012%, and Mn: 0.05% to 1.00 %, and S and Se: 0.003% to 0.015% in total, and the balance consists of Fe and impurities.

Hereinafter, the reason for limitation of a typical example of the chemical composition of a slab and the cold-rolled steel plate obtained by it is demonstrated.

a. Si: 0.80% to 7.00%

Si is an essential component and increases electrical resistance to decrease iron loss. Moreover, by containing Si at a high concentration, strong chemical affinity is expressed between the intermediate|middle layer which has silicon oxide as a main body, and an intermediate|middle layer and a mother steel plate closely_contact|adhere more strongly. However, when content of Si exceeds 7.00 %, cold rolling becomes very difficult, and it becomes easy to generate|occur|produce a crack at the time of cold rolling. For this reason, it is preferable to make content of Si into 7.00 % or less. More preferably, it is 4.50 % or less, More preferably, it is 4.00 % or less.

On the other hand, when the Si content is less than 0.80%, γ transformation occurs during the finish annealing, and the grain orientation of the grain-oriented electrical steel sheet is impaired. For this reason, it is preferable that content of Si shall be 0.80 % or more. More preferably, it is 2.00 % or more, More preferably, it is 2.50 % or more.

b. C: 0.085% or less

C is an element effective for controlling the primary recrystallization structure, but adversely affects magnetic properties. For this reason, decarburization annealing is performed before finish annealing. When there is more C content than 0.085 %, decarburization annealing time will become long, and productivity in industrial production will be impaired. From these points, it is preferable that the content of C is 0.085% or less. Although it does not specifically limit as a lower limit of C content, It is preferable that it is 0.020 % or more, and, as for C content, it is more preferable that it is 0.050 % or more.

c. Acid soluble Al: 0.010% to 0.065%

Acid-soluble Al combines with N to precipitate as (Al, Si)N, and functions as an inhibitor. When the content of acid-soluble Al is within the range of 0.010% to 0.065%, secondary recrystallization is stable. For this reason, the content of acid-soluble Al is preferably 0.010% to 0.065%. In addition, as will be described later, Al is concentrated on the surface of the steel sheet in finish annealing, and this is utilized as Al in Al and Mg present on the surface of the steel sheet when forming the intermediate layer in the method for manufacturing a grain-oriented electrical steel sheet of the present invention described later. From such viewpoints, the content of acid-soluble Al is preferably 0.015% or more, and more preferably 0.020% or more. Moreover, from a viewpoint of stability of secondary recrystallization, it is more preferable that it is 0.050 % or less, and, as for acid-soluble Al content, it is more preferable that it is 0.035 % or less.

d. N: 0.004% to 0.012%

N functions as an inhibitor in combination with Al. If the N content is less than 0.004%, a sufficient amount of inhibitor cannot be obtained. For this reason, it is preferable to make N content into 0.004 % or more. More preferably, it is 0.005 % or more, More preferably, it is 0.006 % or more.

On the other hand, when content of N exceeds 0.012 %, it will become easy to generate|occur|produce the defect called a blister in a steel plate. For this reason, it is preferable to make N content into 0.012 % or less. More preferably, it is 0.011 % or less, More preferably, it is 0.010 % or less.

e. Mn: 0.05% to 1.00%

f. S and Se: 0.003% to 0.015% in total

Mn together with S and/or Se forms MnS and/or MnSe, so that the complex compound functions as an inhibitor. When the content of Mn is in the range of 0.05% to 1.00%, secondary recrystallization is stable. For this reason, it is preferable that content of Mn shall be 0.05 % - 1.00 %. As for content of Mn, it is more preferable that it is 0.08 % or more, and it is still more preferable that it is 0.09 % or more. Moreover, as for content of Mn, it is more preferable that it is 0.50 % or less, and it is still more preferable that it is 0.20 % or less.

When the contents of S and Se are in the range of 0.003% to 0.015% in total, secondary recrystallization is stable. For this reason, it is preferable that content of S and Se shall be 0.003 % - 0.015 % in total.

Here, "the content of S and Se is 0.003% to 0.015% in total" means that the mother steel sheet contains only either S or Se, and the content of either S or Se is 0.003% to 0.015% in total. It means both the case and the case where the mother steel sheet contains both S and Se, and the content of S and Se is 0.003% to 0.015% in total.

g. other elements

In consideration of the enhancement of the inhibitor function due to the formation of the compound or the influence on the magnetic properties, various kinds of elements may be contained in accordance with known literatures instead of a part of the remaining Fe. As a target of the type and content of elements to be contained in place of a part of Fe, for example, "Bi: 0.010% or less", "B: 0.080% or less", "Ti: 0.015% or less", "Nb: 0.20% or less" , "V: 0.15% or less", "Sn: 0.10% or less", "Sb: 0.10% or less", "Cr: 0.30% or less", "Cu: 0.40% or less", "P: 0.50% or less", " Ni: 1.00% or less", "Mo: 0.10% or less", etc. are mentioned.

h. balance

The remainder consists of Fe and impurities. "Impurity" means an element mixed from a component contained in a raw material when manufacturing a mother steel plate industrially, or a component mixed in the process of manufacture.

The slab is obtained, for example, by melting steel having the above-described chemical composition with a converter or an electric furnace, vacuum degassing as necessary, followed by continuous casting or ingot followed by ingot rolling. Although the thickness of a slab is not specifically limited, For example, it is 150 mm - 350 mm, It is preferable that it is 220 mm - 280 mm. Moreover, a slab (so-called "thin slab") having a thickness of about 10 mm to 70 mm may be used. When a thin slab is used, rough rolling before finish rolling can be omitted in the hot rolling process.

<Hot rolling process>

In a hot rolling process, after heating the slab containing Si as mentioned above in the temperature range of 800 degreeC - 1300 degreeC, for example, it hot-rolls and obtains a hot-rolled steel sheet.

By setting the heating temperature of the slab to 1200°C or less, it is preferable because, for example, various problems when heating at a temperature higher than 1200°C (requiring a dedicated heating furnace, large amount of molten scale, etc.) can be avoided. do.

When heating temperature is too low, hot rolling may become difficult and productivity may fall. Therefore, it is preferable that the lower limit of the heating temperature of the slab is 950°C. It is also possible to omit the slab heating process itself and start hot rolling after casting until the temperature of the slab is lowered.

In a hot rolling process, it is set as the hot-rolled steel plate of predetermined thickness by rough-rolling to the slab after heating, and also performing finish rolling. After finish rolling is completed, the hot-rolled steel sheet is wound at a predetermined temperature.

In addition, although the plate|board thickness of a hot-rolled steel plate is not specifically limited, For example, you may be 3.5 mm or less.

<Hot-rolled sheet annealing process>

In the hot-rolled sheet annealing process, hot-rolled sheet annealing is performed to a hot-rolled steel sheet, and an annealed steel sheet is obtained. Although the hot-rolled sheet annealing conditions should just be general conditions, it hold|maintains for 30 second - 10 minutes at the temperature within the range of 750-1200 degreeC, for example.

<Cold rolling process>

In a cold rolling process, cold rolling is performed to an annealed steel plate once or 2 times or more with intermediate annealing, and a cold rolled steel plate is obtained.

Although the cold rolling rate (final cold rolling rate) in the final cold rolling is not specifically limited, From a viewpoint of crystal orientation control, it is preferable to set it as 80 % or more, It is more preferable to set it as 90 % or more.

The thickness of the cold-rolled steel sheet is not particularly limited, but in order to further reduce iron loss, it is preferably 0.35 mm or less, and more preferably 0.30 mm or less.

2. Decarburization annealing process

In the decarburization annealing step, decarburization annealing is performed on the cold rolled steel sheet to obtain a decarburization annealing steel sheet.

Specifically, by performing decarburization annealing, primary recrystallization is generated in the cold-rolled steel sheet, C contained in the cold-rolled steel sheet is removed, and the carbon content of the steel sheet after decarburization annealing is set to 25 ppm or less. It is preferable to perform decarburization annealing in a wet atmosphere in order to remove C. Moreover, in the decarburization annealing process, the oxygen amount after decarburization annealing is controlled to 320 ppm or less by suppressing oxidation.

Hereinafter, a decarburization annealing method included in the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment will be described in detail.

In the grain-oriented electrical steel sheet, about 500 to 600 ppm of carbon is added in order to obtain a texture for improving magnetism. However, since carbon (C) becomes unnecessary after the above-mentioned cold rolling process, in the decarburization annealing process, it is necessary to remove the amount of carbon after annealing to a level which does not generate self-aging in final products, such as a transformer. In a grain-oriented electrical steel sheet having a forsterite film, since it is necessary to form an oxide layer having fayalite on the surface layer of the steel sheet, the cold-rolled steel sheet is usually annealed at a dew point of 60 to 70°C and a soaking temperature of 800 to 900°C.

However, in a grain-oriented electrical steel sheet that does not substantially have a forsterite film like the grain-oriented electrical steel sheet of the present embodiment, when annealing under the high dew point conditions as described above, an oxide (mullite) is formed during high-temperature annealing. , the surface smoothness is lowered by oxidation of the steel sheet, and the magnetic properties are lowered. In addition, when the dew point is reduced in order to avoid this, according to the studies of the present inventors, it became clear that the decarburization rate decreased, the amount of residual carbon increased, and self-aging occurred. That is, since decarburization promotion and oxidation inhibition of a steel sheet are opposite phenomena in establishing atmospheric conditions, it is difficult to realize the decarburization annealing dew point under constant conditions.

The present inventors thought that it would be possible to achieve both decarburization and oxidation inhibition by minimizing oxidation after completion of decarburization by first performing decarburization at a high dew point as a decarburization annealing treatment, and then lowering the decarburization point. Based on this thought, the present inventor conducted the following experiment and investigated the influence of dew point control in the first half of the decarburization annealing process and the dew point control in the second half of the decarburization annealing process.

This experiment was conducted using a decarburization annealing furnace equipped with a box-shaped heating furnace 1 and a crack furnace 2 having the configuration shown in Figs. 4A and 4B.

As shown in Figs. 4A and 4B, the inside of the heating furnace 1 is a heating zone, and the inside of the cracking furnace 2 is a crack zone, from the heating zone to the right side indicated by the arrows shown in Figs. 4A and 4B. It is a decarburization annealing furnace which can horizontally convey a steel plate in a direction and can perform a decarburization annealing process with respect to a steel plate in the middle of conveyance.

The decarburization annealing furnace shown in FIG. 4A is a furnace capable of supplying atmospheric gas in the direction opposite to the passage direction of the steel sheet into the inside of the cracking furnace 2 from the side wall part (the rear end of the crack zone) near the exit of the cracking furnace 2 .

In the decarburization annealing furnace shown in Fig. 4B, an atmospheric gas can be supplied into the inside of the cracking furnace 2 from the side wall portion (rear end of the crack zone) near the outlet of the cracking furnace 2 in the direction opposite to the passing direction of the steel sheet. , It is a decarburization annealing furnace capable of supplying atmospheric gas in the direction opposite to the conveying direction of the steel sheet from the bottom (front end of the crack zone (the rear end of the heating zone)) near the inlet of the cracking furnace 2 toward the heating furnace 1 side.

In the present embodiment, the front end of the crack zone means a position on the side of the heating zone (upstream side) from the center of the crack zone, and the rear end of the crack zone means a position on the downstream side from the center of the crack zone, and is a position shown in Fig. 4B, for example. The position at which atmospheric gas is introduced is preferably near the entrance of the crack zone (crack temperature reached position) at the front end, and near the exit of the crack zone at the rear end.

<Experiment 1>

In this embodiment, using the decarburization annealing furnace shown in FIG. 4B, under the processing conditions shown in Table 1 below, an atmospheric gas having a dew point DP1 of 30 to 70° C. is introduced from the front end of the crack zone, and further, the crack zone A test was conducted in which the dew point (DP2) of the atmospheric gas introduced from the rear end was changed to -20 to 50°C. Subsequently, the obtained decarburization annealing steel sheet was subjected to nitriding treatment under the nitriding treatment conditions shown in Table 1, and the carbon content and oxygen amount of the decarburization annealed steel sheet were investigated. About the amount of carbon in the obtained steel plate, it was set as CO gas by burning in oxygen stream, and it analyzed using the infrared absorption method. Regarding the amount of oxygen, CO gas was obtained by burning the sample in a graphite crucible in an inert gas such as He, and this was analyzed by an infrared absorption method.

A magnesia water slurry may be applied to the obtained decarburization annealed steel sheet as in the prior art, but in this example, since it reacts with silica in the finish annealing process, irregularities in the surface oxide layer occur. In this experiment, alumina is used as the main component (For example, MgO: about 10 to 50%, Al ₂ O ₃ : 90 to 50% is included) Water slurry application was performed using an annealing separator.

Next, finish annealing was performed, further tension coating was applied, and thereafter, magnetic domain refining was performed by laser irradiation to obtain a plurality of grain-oriented electrical steel sheets. For these grain-oriented electrical steel sheets, magnetic properties (core loss W17/50 at 1.7T and 50 Hz and magnetic flux density B8 at 800 A/m of magnetization force) were measured based on the Epstein method described in JISC2550-1:2011. did.

Fig. 1 shows the relationship between the oxygen content of the obtained steel sheet and magnetic properties.

From Fig. 1, when the oxygen content of the steel sheet exceeded 320 ppm, it was found that the iron loss deteriorated in any of the samples. This is because, when the oxidation amount in decarburization annealing exceeds 320 ppm, oxide (mullite) is formed during high-temperature annealing, and the smoothness of the steel sheet is lost, thereby reducing iron loss.

In addition, Fig. 2 shows the relationship between the aging time, the carbon content of the steel sheet, and the magnetic flux density obtained after holding for a maximum of 10 days while annealing at 150°C. It became clear from FIG. 2 that the holding force deteriorated rapidly in the sample whose carbon amount of steel plate exceeds 25 ppm. This is considered to be because carbides and nitrides are precipitated by aging, and these interfere with the movement of magnetic domain walls.

Next, in this embodiment, the dominant factor of decarburization and oxidation reaction was clarified, and the technique for making decarburization and oxidation compatible at the time of low-dew point decarburization annealing was examined.

It is known that the rate of decarburization reaction in the steel sheet is the rate of diffusion of carbon in the steel sheet, and it is known that the decarburization reaction starts at about 700°C or higher. Therefore, in 700 degreeC or more, it is thought that improving the decarburization temperature, decarburization time, and gas oxidation degree of atmospheric gas becomes important in improving decarburization property.

In Non-Patent Document 1, when a 3% Si steel sheet is annealed at 850°C, _{the influence of the gas oxidation degree (P H2O} /P _H2 ) on the oxidation of the steel sheet is described (see FIG. 3 ). As shown in FIG. 3 , when the gas oxidation degree (P _H2O /P _H2 ) is 0.02 (in the case of a 75% hydrogen atmosphere, the dew point is equivalent to 18°C) or less, the oxide formed on the surface of the steel sheet is mainly SiO ₂ . Because the SiO ₂ is amorphous, it is known that the gas penetration effect is very small. _{In addition, since SiO 2} is preferentially formed when annealing at a low dew point in a low-temperature portion, it is important to anneal at a relatively high dew point in the early stage of oxidation to suppress the formation of _{SiO 2 for improvement of decarburization.} can

4C, the atmospheric gas dew point distribution (dotted line) in the furnace when atmospheric gas is introduced from the rear end of the crack zone in the decarburization annealing furnace as shown in FIG. 4A, and the atmospheric gas from two places of the heating zone and the crack zone as shown in FIG. 4B A schematic diagram of the atmospheric gas dew point distribution (solid line) in the furnace in one case is shown.

As shown in FIG. 4A , when atmospheric gas is collectively introduced from the rear end of the crack zone 2, water vapor in the atmospheric gas is consumed while flowing from the crack zone 2 toward the heating zone 1 side. It can be seen that the dew point of the atmospheric gas introduced from the rear end of the stage 2 decreases toward the direction of the heating stage 1 as indicated by the dotted line in FIG. 4C . The dew point is lowered, is thereby promotes the formation of amorphous SiO _2, it makes it more difficult to balance the decarburization and oxidation. In addition, since decarburization is completed when the cracking temperature is reached, it is effective to supply an atmospheric gas having a high dew point before reaching the cracking temperature in order to promote decarburization.

On the other hand, if the introduction of the atmospheric gas from gayeoldae and cracks cause in two places as shown in Figure 4b, by introducing a high dew point gas at the front, by suppressing the formation of the amorphous SiO _2, it is possible to promote the decarburization reaction. On the other hand, excessive oxidation of Si after decarburization can be suppressed by introducing a low dew point gas at the rear stage.

From the above consideration, in this embodiment, as shown by the solid line in FIG. 4B , in order to promote decarburization at the front end (cracking temperature reaching point) of the cracking zone 2, an atmospheric gas having a high dew point DP1 is introduced, and further cracking It was thought that coexistence of decarburization and oxidation suppression was attained by the two-step gas introduction of introduce|transducing the atmospheric gas of low dew point (DP2) in order to suppress excessive oxidation from the rear stage of the stand (2).

<Experiment 2>

The present inventors have used the decarburization annealing furnace 10 shown in FIG. 4B to promote decarburization in the heating zone 1 and control oxidation in the crack zone 2 under the processing conditions shown in Table 2 below, An experiment was conducted in which the decarburization annealing conditions were changed during annealing. The cracking temperature at the time of decarburization annealing is determined as a condition in which the decarburization and oxidation amount of the decarburization annealing steel sheet are compatible, and may be carried out at 800 to 870 ° C., preferably 805 to 850 ° C., more preferably 820 to 835 ° C. .

The obtained decarburization annealed steel sheet was subjected to the nitridation annealing described in Table 2, a water slurry application using an annealing separator containing alumina as a main component was applied to finish annealing, and a plurality obtained by performing magnetic domain refining by laser irradiation after tension coating application. Magnetic properties were measured for the grain-oriented electrical steel sheet. About magnetic measurement, based on the Epstein method described in JISC2550-1:2011, the magnetic flux density B8 in 1.7T and 50 Hz iron loss W17/50 and 800 A/m of magnetization force was evaluated.

Fig. 5 shows the test results. In FIG. 5 , ○ indicates an example in which the magnetic target is satisfied, and × indicates an example in which the magnetic target is not satisfied. From the test results shown in Fig. 5, it was found that good magnetic properties were obtained under the conditions of DP1 of 40 to 70 DEG C, DP2 ? DP1, and 60-DP1 ? DP2 ? 100-DP1.

That is, when the oxygen content after decarburization annealing is 320 ppm or less and the carbon content is 25 ppm or less to obtain good magnetic properties, DP1 is 40 to 70° C., DP2 ≤ DP1, and 60-DP1 ≤ DP2 ≤ 100-DP1. It is preferable to perform decarburization annealing in

When DP1 is less than 40°C, decarburization of the thick material becomes difficult, and when DP1 is above 70°C, oxidation of the thin material becomes excessive. In the case of a thick material, it is more preferably 50 to 70°C, and in the case of a thin material, it is more preferably 40 to 60°C.

Further, in the case of DP2>DP1, the progress of decarburization in the heating zone is delayed, and oxidation in the crack zone in which the plate temperature rises compared to the heating zone proceeds, so that decarburization is inhibited. Therefore, it is preferable to set DP2 ? DP1.

Moreover, when DP2 is less than (60-DP1), decarburization after decarburization annealing becomes inadequate, and when DP2 is more than (100-DP1), it becomes excessive oxidation of a thin-walled material. Therefore, it is preferable that DP2 be in the range of 60-DP1 ? DP2 ? 100-DP1.

3. Finish annealing process, removal process

In the finish annealing step, the steel sheet is subjected to finish annealing. Thereby, secondary recrystallization is generated in a steel plate.

In a general grain-oriented electrical steel sheet, _{since a finish annealing film containing forsterite (Mg 2} SiO ₄ ) as a main component is formed, the magnesia concentration is generally high on the surface of the decarburization annealed steel sheet (for example, MgO≥90 mass%). ) by applying an annealing separator to perform a final annealing process.

In contrast, in the finish annealing step of the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment, an annealing separator containing aluminum oxide with a low magnesia concentration on the surface of the decarburized annealing steel sheet (eg, MgO: 10 to 50) About mass %, Al ₂ O ₃ : In a state in which 90 to 50 mass % is included), finish annealing is performed by heating (secondary recrystallization), and then finishing by removing excess annealing separation material. Obtain annealed steel sheet. By these, forsterite to form an intermediate layer so that the finish annealing film is formed consisting of (Mg ₂ SiO _4).

Here, the annealing separator is applied to prevent seizing between steel sheets after final annealing and to form a finish annealing film made _{of forsterite (Mg 2} SiO _{4 ).} In the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment, since it is necessary to form an intermediate layer so as not to form a finish annealing film made _{of forsterite (Mg 2} SiO _{4 ), an annealing separator having a low magnesia concentration is used.}

The heating conditions for the finish annealing may be general conditions, for example, heating rate: 5°C/s to 100°C/s, and heating at a temperature within the range of 1000°C to 1300°C for 10 hours to 50 hours.

At the time of cooling after the said heating, it can cool from 1100 degreeC to 500 degreeC in the atmosphere of _{the oxidation degree of gas (P H2O} /P _{H2):0.0001-100000.}

More specifically, in the cooling process after reaching the maximum temperature of the finish annealing process, when the maximum temperature is 1100 ° C. or higher, T1 is 1100 ° C., when the maximum temperature is less than 1100 ° C., T1 is the maximum temperature. , T1 to 500 ℃ temperature range, the oxidation degree of the gas (P _H2O /P _H2 ): can be cooled in an atmosphere of 0.0001 to 100000, but is not limited to these conditions. Preferably, the gas oxidation degree is between 0.3 and 100000.

Although there is no restriction|limiting in particular for the cooling time to cool under the said conditions, It is preferable to set it as 5 to 30 hours.

After cooling, the finish annealing steel sheet can be obtained by removing the annealing separator. Although there is no restriction|limiting in particular with respect to the removal method of an annealing separator, It can remove to the extent of rubbing the surface of a mother steel plate with a brush.

4. Interlayer Forming Process

In the intermediate layer forming step, for example, after heating the finish annealing steel sheet to an upper limit temperature region exceeding 600° C., the steel sheet is heated to a temperature region exceeding 600° C. and below the upper limit temperature, the gas oxidation degree (P H _O /P _H2 ): An intermediate layer containing silicon oxide as a main component can be formed on the surface of the finish-annealed steel sheet by annealing while maintaining it in an atmosphere of 0.001 to 0.04.

The intermediate layer is "A. Grain-oriented electrical steel sheet 2. It is preferable to form to the thickness described in the item of "Intermediate layer".

In the intermediate layer forming step, the heating conditions of the finish annealed steel sheet are not particularly limited as long as they are heated to a temperature range of more than 600 ° C., for example, in a temperature range of 700 ° C. to 1150 ° C. for 10 seconds to 60 seconds. It is preferable to carry out under conditions. From the viewpoint of the reaction rate, the temperature needs to exceed 600°C, but when the temperature is higher than 1150°C, it is difficult to keep the formation reaction of the intermediate layer uniformly, so that the interface between the intermediate layer and the mother steel sheet becomes severe and the iron loss deteriorates. , the strength of the steel sheet is lowered, and processing in a continuous annealing furnace becomes difficult, and thus productivity may be lowered.

The holding time is preferably set to 10 seconds or longer from the viewpoint of forming the intermediate layer, and is preferably set to 60 seconds or less from the viewpoint of avoiding a decrease in productivity and the space factor due to an increase in the thickness of the intermediate layer.

From the viewpoint of forming the intermediate layer to a thickness of 2 to 400 nm, it is preferable to hold for 15 to 60 seconds in a temperature range of 650 to 1000°C, and more preferably hold for 25 to 60 seconds in a temperature range of 700 to 900°C. .

5. Insulation film formation process

In the insulating film forming step, after applying and baking a coating solution on the surface of the intermediate layer, for example, an insulation film is applied to the surface of the intermediate layer by heating in a temperature range of 700°C to 1150°C for 5 to 60 seconds in an atmosphere of 100% nitrogen gas. to form

The insulating film is the above-mentioned "A. Grain-oriented electrical steel sheet 1-3. It is preferable to form a film with the thickness described in the item of "Insulation film".

The coating solution is not particularly limited, but a coating solution having colloidal silica and a coating solution not having colloidal silica may be used separately depending on the application.

As a coating solution which does not have colloidal silica, the coating solution containing alumina and boric acid is mentioned, for example.

Moreover, as a coating solution which has colloidal silica, the coating solution containing phosphoric acid or a phosphate, colloidal silica, and chromic anhydride or chromate is mentioned, for example. Examples of the chromate include chromate salts such as Na, K, Ca, and Sr. There is no limitation in particular for colloidal silica, The particle size can also be used suitably.

In addition, in order to improve various characteristics, you may further add various elements and compounds to a coating solution, unless the effect requested|required by this embodiment is lost.

In the insulating film forming step, heating and annealing may be performed to 650 to 950°C in an atmosphere of _{gas oxidation degree (P H2O} /P _{H2 ): 0.01 to 0.30.} As said gas, what is necessary is just to be a gas normally used, For example, the gas which consists of hydrogen: 25 volume% and balance: nitrogen and an impurity can be used.

During cooling of the insulating film forming process, if the oxidation degree of the gas (P _H2O /P _H2 ) is less than 0.01, the insulating film may be decomposed. have. The degree of oxidation of the gas (P _H2O /P _H2 ) is more preferably 0.02 to 0.08, and still more preferably 0.03 to 0.05.

6. Other processes

The method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment may further include a process generally performed in the method for manufacturing a grain-oriented electrical steel sheet, from the start of decarburization annealing to the expression of secondary recrystallization in finish annealing. In the meantime, it is preferable to further have a nitriding treatment step of performing a nitriding treatment for increasing the N content of the decarburization annealed steel sheet. This is because the magnetic flux density can be stably improved even when the temperature gradient provided to the steel sheet at the boundary between the primary recrystallization region and the secondary recrystallization region is low. The nitriding treatment may be a general treatment. For example, annealing in an atmosphere containing a gas having a nitriding ability such as ammonia, or finish annealing a decarburization annealed steel sheet coated with an annealing separator containing a powder having a nitriding ability such as MnN processing and the like.

B-2. second embodiment

In the first embodiment, the process for the purpose of forming the intermediate layer, which is individually provided, and the process for the purpose of only forming the insulating film were performed separately. In the second embodiment, the intermediate layer and the insulating film are formed at the same time. different from the embodiment. That is, it differs from the first embodiment in that the following intermediate layer-insulating film forming step is performed instead of the above-described intermediate layer forming step and insulating film forming step.

For that reason, only the intermediate layer-insulating film forming process will be described below.

1. Interlayer-insulation film forming process

By applying a coating solution to the surface of the finish annealing steel sheet, for example, in a temperature range of more than 650 ° C. to 950 ° C. or less, the oxidation degree of gas ( _{P H 2 O} /P H 2 ): 5 to 300 seconds annealing in an atmosphere of 0.01 to 0.30 By doing so, an intermediate layer and an insulating film containing silicon oxide as a main component are simultaneously formed on the surface of the finish-annealed steel sheet.

When a coating solution is applied to the surface of a finish annealed steel sheet and heat treated, an intermediate layer and a metallic Fe phase are formed on the surface of the steel sheet by reducing Fe in the Fe-based oxide, and at the same time, an insulating film is formed on the surface of the intermediate layer by baking the coating solution.

In order to simultaneously advance the formation of the intermediate layer by thermal oxidation and the formation of the insulating film by baking of the coating solution, it is more preferable to set the gas _{oxidation degree (P H2O} /P _{H2 ): 0.05 to 0.25, and} Oxidation degree (P _H2O /P _H2 ): It is more preferable to set it as the condition of 0.10-0.20.

The present invention is not limited to the above-described embodiment. The above-mentioned embodiment is an illustration, and any thing which has substantially the same structure as the technical idea described in the claim of this invention, and exhibits the same operation and effect is included in the technical scope of this invention.

Example

Hereinafter, the present invention will be specifically described by way of examples. In the following, the conditions in the examples are examples of conditions employed in order to confirm the feasibility and effect of the present invention, and the present invention is not limited to these examples. Various conditions can be employ|adopted for this invention, as long as the objective of this invention is achieved without deviating from the summary of this invention.

<Example 1>

“When the plate thickness is 0.18 mm”

Si: 3.45%, C: 0.060%, acid soluble Al: 0.030%, N: 0.008% and Mn: 0.10%, and S and Se: 0.007% in total, the balance being Fe and impurities. After cracking a slab at 1150 degreeC for 60 minutes, it hot-rolled to the slab after heating, and obtained the hot-rolled steel plate whose plate|board thickness is 2.8 mm. Next, after hold|maintaining a hot-rolled steel sheet at 900 degreeC for 120 second, the hot-rolled sheet annealing was performed by rapid cooling, and the annealed steel sheet was obtained. Next, after pickling the annealed steel sheet, cold rolling was performed once or several times to the steel sheet after pickling, and the cold-rolled steel sheet whose final sheet thickness is 0.18 mm was obtained.

Using this thin-walled cold-rolled steel sheet (thickness 0.18 mm), as shown in Table 3, the soaking temperature was set to 820 to 835° C. carried out. At that time, the dew point DP1 of the atmospheric gas introduced from the front stage was changed to 30 to 80°C, and the dew point DP2 of the atmospheric gas introduced from the rear stage was changed to -5 to 55°C. The target amount of carbon [C] was 25 ppm or less, and the amount of oxygen [O] was 320 ppm or less.

About the amount of carbon after decarburization annealing, it was set as CO gas by burning in oxygen stream, and it analyzed using the infrared absorption method. Regarding the amount of oxygen, CO gas was obtained by burning the sample in a graphite crucible in an inert gas such as He, and this was analyzed by an infrared absorption method.

After decarburization annealing, an annealing separator containing alumina, which is difficult to react with silica, as a main component was applied as a water slurry, and then finish annealing was performed. Finish annealing N ₂ up to _{1200 ℃: 25% + H 2} : 75% is performed at a heating rate of 15 ℃ / Hr from the atmosphere gas, H ₂ eseo 1200 ℃: was carried out for 20 hours annealing by switching to 100%. At the time of cooling after the said heating, it cooled from 1100 degreeC to 500 degreeC in the atmosphere of _{the oxidation degree of gas (P H2O} /P _{H2):0.0001-100000.} In addition, the cooling time for cooling under the above conditions was set to 5 to 30 hours.

The annealing separator material of the steel sheet after these finish annealing is removed with a brush, and for some steel sheets, annealing is performed at 870° C. and an atmosphere in which the degree of oxidation of the atmospheric gas (P _H2O /P _H2 ) is 0.01 for 60 seconds, whereby the thickness is 20 nm A phosphorus intermediate layer was formed. After cooling the steel sheet, after applying the coating solution, annealing for 60 seconds in an atmosphere of 840 ° C., the oxidation degree of the atmospheric gas (P _H2O /P _H2 ) is 0.03, the adhesion amount after baking 4.5 g / m 2, the thickness is 2㎛ An insulating film was formed.

In addition, for other steel sheets, after application of the coating solution, drying at 450 ° C., followed by annealing for 60 seconds in an atmosphere of _{840 ° C. and atmospheric gas oxidation (P H 2 O} /P H 2 ) 0.10, a thickness of 20 nm An insulating film having a phosphorus intermediate layer and an adhesion amount of 4.5 g/m 2 and a thickness of 2 μm after baking was formed.

Finally, the magnetic domain refining process was performed with a laser so that the linear groove|channel extending in the direction intersecting the rolling direction might become a predetermined space|interval.

Thereafter, magnetic measurement was performed on the obtained grain-oriented electrical steel sheet. About magnetic measurement, based on the Epstein method described in JISC2550-1:2011, the magnetic flux density B8 in 1.7T and 50 Hz in iron loss W17/50 and 800 A/m of magnetization force was evaluated. Regarding the evaluation of the magnetic properties, it was judged that the iron loss W17/50 was less than 0.60 W/kg and the magnetic flux density was more than 1.60 T as favorable.

The test results are shown in Table 3 below.

The thin-walled material has better de-elasticity compared to the thick-walled material, whereas oxidation tends to proceed, so good magnetic properties were not obtained when the shear dew point DP1 was 30°C and 80°C.

Further, as shown in Table 3, in the example of the present invention, in the steel sheet after decarburization annealing, a decarburization annealing steel sheet having an oxygen content of 320 ppm or less and a carbon content of 25 ppm or less was obtained. In particular, when the dew point DP1 of the atmospheric gas introduced from the front end of the cracking zone is 40 to 70° C. and the dew point DP2 of the atmospheric gas introduced from the rear end of the cracking zone is DP2≦DP1 and 60-DP1≦DP2≦100-DP1, A decarburization annealed steel sheet having an oxygen content of 320 ppm or less and a carbon content of 25 ppm or less was obtained. And the grain-oriented electrical steel sheet obtained by forming an intermediate layer and an insulating layer using these decarburization-annealed steel sheets was an excellent electrical steel sheet with low iron loss. Moreover, the film adhesiveness was sufficient in any example.

<Example 2>

"When the plate thickness is 0.23 mm"

Si: 3.45%, C: 0.060%, acid soluble Al: 0.030%, N: 0.008% and Mn: 0.10%, and S and Se: 0.007% in total, the balance being Fe and impurities. After cracking a slab at 1150 degreeC for 60 minutes, it hot-rolled to the slab after heating, and obtained the hot-rolled steel plate whose plate|board thickness is 2.8 mm.

Next, after hold|maintaining a hot-rolled steel sheet at 900 degreeC for 120 second, the hot-rolled sheet annealing was performed by rapid cooling, and the annealed steel sheet was obtained. Next, after pickling the annealed steel sheet, cold rolling was performed once or several times to the steel sheet after pickling, and the cold-rolled steel sheet whose final sheet thickness is 0.23 mm was obtained.

Decarburization annealing was performed using a cold-rolled steel sheet having a thickness of 0.23 mm, a cracking temperature of 820 to 840 ° C, a shear dew point DP1 of 30 to 80 ° C, and a rear dew point DP2 of -15 to 55 ° C.

After decarburization annealing, an annealing separator containing alumina, which is difficult to react with silica, as a main component was applied as a water slurry, and then finish annealing was performed. Finish annealing N ₂ up to _{1200 ℃: 25% + H 2} : 75% gas atmosphere is performed in 15 ℃ / heating rate of time of from, H ₂ eseo 1200 ℃: was carried out for 20 hours annealing by switching to 100%. At the time of cooling after the said heating, it cooled from 1100 degreeC to 500 degreeC in the atmosphere of _{the oxidation degree of gas (P H2O} /P _{H2):0.0001-100000.} In addition, the cooling time for cooling under the above conditions was set to 5 to 30 hours.

The annealing separation material of the steel sheet after these finish annealing is removed with a brush, and for some steel sheets, the thickness is 20 nm by annealing for 60 seconds in an atmosphere of _{870° C. and an atmosphere gas oxidation (P H2O} /P _{H2 ) of 0.010.} A phosphorus intermediate layer was formed. After cooling the steel sheet, after applying a coating solution, annealing for 60 seconds in an atmosphere of 840 ° C. and an atmosphere of which the degree of oxidation (P _H2O / P _{H2 ) of the atmospheric gas is 0.01.} An insulating film was formed. In addition, for other steel sheets, an intermediate layer having a thickness of 20 nm and an adhesion amount after baking 4.5 g/m 2 by annealing for 60 seconds in an atmosphere of 870 ° C. and an atmospheric gas oxidation degree (P _{H 2 O} /P H 2 ) of 0.10, An insulating film having a thickness of 2 mu m was formed.

Finally, the magnetic domain refining process was performed with a laser so that the linear groove|channel extending in the direction crossing the rolling direction might become a predetermined space|interval.

Thereafter, magnetic measurement was performed on the obtained grain-oriented electrical steel sheet. About magnetic measurement, based on the Epstein method described in JISC2550-1:2011, the magnetic flux density B8 in 1.7T and 50 Hz iron loss W17/50 and 800 A/m of magnetization force was evaluated.

Regarding the evaluation of the magnetic properties, it was judged that the iron loss W17/50 was less than 0.70 W/kg and the magnetic flux density was more than 1.60 T as favorable. A result is shown in Table 4.

As the test results are shown in Table 4, when the coexistence conditions of oxidation and decarburization are wider than that of the steel plate of the plate thickness shown in Table 3, and the shear dew point DP1 is 40 to 70°C, there are conditions in which good magnetic properties are obtained.

As shown in Table 4, in the example of the present invention, in the steel sheet after decarburization annealing, a decarburization annealing steel sheet having an oxygen content of 320 ppm or less and a carbon content of 25 ppm or less was obtained. And the grain-oriented electrical steel sheet obtained by forming an intermediate layer and an insulating layer using these decarburization-annealed steel sheets was an excellent electrical steel sheet with low iron loss.

In addition, by satisfying the relationship of DP2≤DP1 and 60-DP1≤DP2≤100-DP1, an excellent grain-oriented electrical steel sheet with an oxygen content of 320 ppm or less, and a carbon content of 25 ppm or less and low iron loss is a steel sheet with a thickness of 0.23 mm thicker than 0.18 mm It was found that it can also be obtained in

<Example 3>

"When the plate thickness is 0.35 mm"

Si: 3.25%, C: 0.050%, acid soluble Al: 0.030%, N: 0.008%, and Mn: 0.10%, and S and Se: 0.006% in total, the balance being Fe and impurities. After cracking a slab at 1150 degreeC for 60 minutes, it hot-rolled to the slab after heating, and obtained the hot-rolled steel plate whose plate|board thickness is 2.8 mm.

Next, after hold|maintaining a hot-rolled steel sheet at 900 degreeC for 120 second, the hot-rolled sheet annealing was performed by rapid cooling, and the annealed steel sheet was obtained. Next, after pickling the annealed steel sheet, cold rolling was performed once or several times to the steel sheet after pickling, and the cold-rolled steel sheet whose final sheet thickness is 0.35 mm was obtained.

Using a cold-rolled steel sheet of thick material (thickness 0.35 mm), decarburization annealing is performed with a cracking temperature of 820 to 840 ° C, a shear dew point DP1 of 30 to 80 ° C, and a rear dew point DP2 of -15 to 55 ° C. did.

After annealing, an annealing separator containing alumina, which is difficult to react with silica, as a main component was applied as a water slurry, followed by finish annealing. Finish annealing N ₂ up to _{1200 ℃: 25% + H 2} : 75% is performed at a heating rate of 15 ℃ / Hr from the atmosphere gas, H ₂ eseo 1200 ℃: was carried out for 20 hours annealing by switching to 100%.

At the time of cooling after the said heating, it cooled from 1100 degreeC to 500 degreeC in the atmosphere of _{the oxidation degree of gas (P H2O} /P _{H2):0.0001-100000.} In addition, the cooling time to cool under the said conditions was made into 5 to 30 hours.

Removing the anneal separating material of these samples with a brush, and, for some of the steel sheet, 870 ℃, also by annealing 60 seconds at 0.01 atmosphere (P _H2O / P _H2) of the oxidizing gas atmosphere, to the intermediate layer has a thickness 20㎚ formed. After cooling the steel sheet, after applying a coating solution, _{annealing for 60 seconds in an atmosphere of 840 ° C., the oxidation degree (P H2O} / P _H2 ) of the atmospheric gas is 0.01, the adhesion amount after baking 4.5 g / m2, the thickness is 2㎛ An insulating film was formed. In addition, for other steel sheets, after coating the insulating film, drying at 450 ° C., followed by annealing at 840 ° C. for 60 seconds with an _{oxidation degree (PH 2 O} /P _{H 2 ) of the atmospheric gas of 0.10, and a thickness of 20} An intermediate layer of nm and an insulating film having an adhesion amount of 4.5 g/m 2 and a thickness of 2 μm after baking were simultaneously formed.

Finally, the magnetic domain refining process was performed with a laser so that the linear groove|channel extending in the direction crossing the rolling direction might become a predetermined space|interval.

Thereafter, magnetic measurement was performed on the obtained grain-oriented electrical steel sheet. Regarding the evaluation of the magnetic properties, it was judged that the iron loss W17/50 was less than 0.77 W/kg and the magnetic flux density was more than 1.60 T as favorable.

The results are shown in Table 5 below.

From the results shown in Table 5, in the example of the present invention, in the steel sheet after decarburization annealing, a decarburization annealing steel sheet having an oxygen content of 320 ppm or less and a carbon content of 25 ppm or less was obtained. And the grain-oriented electrical steel sheet obtained by forming an intermediate layer and an insulating layer using these decarburization-annealed steel sheets was an excellent electrical steel sheet with low iron loss.

In the thick material, decarburization becomes a neck and causes deterioration of magnetic aging of the final product.

In addition, by satisfying the relationship of DP1 = 40 to 70 ° C, DP2 ≤ DP1 and 60-DP1 ≤ DP2 ≤ 100-DP1, the oxygen content is 320 ppm or less, and the carbon content is 25 ppm or less, and an excellent grain-oriented electrical steel sheet with low iron loss is 0.23 mm It turned out that it can be obtained also in the thicker steel plate of 0.35 mm in thickness.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of a grain-oriented electrical steel sheet which does not have a forsterite film substantially can be provided. In the method for manufacturing a grain-oriented electrical steel sheet according to the above aspect, by achieving both decarburization and steel sheet oxidation suppression in a wide sheet thickness range, a grain-oriented electrical steel sheet with low iron loss and high magnetic flux density after magnetic aging can be manufactured.

1: heating furnace
2: By the crack

Claims (5)

A method of manufacturing a grain-oriented electrical steel sheet having an intermediate layer containing silicon oxide as a main component on a surface of a mother steel sheet substantially free of a forsterite film, and having an insulating film on the surface of the intermediate layer,
A decarburization annealing step of subjecting a cold rolled steel sheet containing Si to decarburization annealing to obtain a decarburization annealing steel sheet having an oxygen content of 320 ppm or less and a carbon content of 25 ppm or less;
a final annealing process of heating the decarburization annealing steel sheet in a state in which an annealing separator is applied to the surface of the decarburization annealing steel sheet to secondary recrystallize the steel sheet;
a removal step of obtaining a finish annealing steel sheet by removing the annealing separator on the steel sheet after the final annealing step;
an intermediate layer forming step of performing thermal oxidation annealing on the finish annealed steel sheet to form the intermediate layer;
An insulating film forming step of forming the insulating film on the finish annealing steel sheet on which the intermediate layer is formed
A method of manufacturing a grain-oriented electrical steel sheet, characterized in that it has a. A method of manufacturing a grain-oriented electrical steel sheet having an intermediate layer containing silicon oxide as a main component on a surface of a mother steel sheet substantially free of a forsterite film, and having an insulating film on the surface of the intermediate layer,
A decarburization annealing step of subjecting a cold rolled steel sheet containing Si to decarburization annealing to obtain a decarburization annealing steel sheet having an oxygen content of 320 ppm or less and a carbon content of 25 ppm or less;
a final annealing process of heating the decarburization annealing steel sheet in a state in which an annealing separator is applied to the surface of the decarburization annealing steel sheet to secondary recrystallize the steel sheet;
a removal step of obtaining a finish annealing steel sheet by removing the annealing separator on the steel sheet after the final annealing step;
Interlayer-insulating film forming process of forming the intermediate layer and the insulating film on the finish annealing steel sheet in one process
A method of manufacturing a grain-oriented electrical steel sheet, characterized in that it has a. 3. The method of claim 1 or 2,
In the decarburization annealing step, an atmospheric gas is introduced into a crack zone for decarburization annealing of the cold-rolled steel sheet from two locations, a front end and a rear end of the crack zone.
A method of manufacturing a grain-oriented electrical steel sheet, characterized in that 4. The method of claim 3,
In the decarburization annealing step, the dew point DP1 of the atmospheric gas introduced from the front end of the cracking zone is 40 to 70°C, and the dew point DP2 of the atmospheric gas introduced from the rear end of the cracking zone is DP2≤DP1 and 60-DP1≤ Made with DP2≤100-DP1
A method of manufacturing a grain-oriented electrical steel sheet, characterized in that 5. The method according to any one of claims 1 to 4,
The cold-rolled steel sheet has, as a chemical component, mass%,
Si: 0.80 to 7.00%,
C: 0.085% or less;
Acid soluble Al: 0.010 to 0.065%,
N: 0.012% or less;
Mn: 1.00% or less;
Sum of S and Se: 0.003 to 0.015%
contains, and the remainder consists of Fe and impurities
A method of manufacturing a grain-oriented electrical steel sheet, characterized in that

Images